Mark Broadie, a professor at Columbia Business School, has helped develop a new methodology for analyzing putting performance that is being introduced by the PGA Tour this week. We asked Broadie to talk about how his system works.
The PGA Tour has announced it will be using your methodology to measure putting. How does your system work?
The new "strokes gained-putting" stat measures the number of putts a golfer takes relative to the PGA Tour average, taking into account the initial putt distance on each green. In 2010 Luke Donald led the Tour with 0.871 strokes gained. That means in each round, he gained an average of 0.871 strokes on the field just from his superior putting ability. Here's how the stat is computed. Suppose, for example, a golfer one-putts from 33 feet. The Tour average to hole-out from that distance is 2.0 putts, so a one-putt gains one putt on the field. A two-putt neither gains nor loses, but a three-putt represents a loss of one putt (or stroke) against the field.
From other distances, the strokes gained or lost are typically fractional. For example, suppose a golfer one-putts from eight feet. The Tour average from that distance is 1.5, so a one-putt gains 0.5 strokes, but a two-putt loses 0.5 strokes. If the golfer started from eight feet 10 times in the round and made half of them, his strokes gained would be zerohe gained 0.5 on five holes and lost 0.5 on the other five holes. If the golfer made six and missed four, his strokes gained would be onehe gained 0.5 on six holes and lost 0.5 on four holes. That makes sense because he took a total of 14 putts vs. the Tour average of 15 putts.
Strokes gained on each hole are added to give total strokes gained for the round, for the tournament, or for a season.
How does your system differ from other putting statistics? In other words, what's new about what you measure?
Putters who start closer to the hole take fewer putts on average, so distance is a primary determinant of putts taken. Unlike other stats, strokes gained-putting explicitly takes into account the initial putt distance on each green, and that makes it a pure measure of putting skill. Other putting stats mix sand skill, short game accuracy and iron play with putting. Putts-per-round rewards a chip-in from off the green because that counts as a zero-putt green. The golfer's putts-per-round stat improves because of a chip shot that had nothing to do with putting performance.
Putts-per-green in regulation (PPGIR) is an indirect attempt to adjust for distance, but it still mixes iron play and putting: Golfers who hit more accurate iron shots tend to have fewer putts per green simply because their putts start closer to the hole. PPGIR isn't easy to interpret: how much better is 1.75 putts per green in regulation compared to 1.80 putts per green in regulation? (Even though it doesn't seem like much, it represents the difference between a rank of 33 or 133, a big difference.)
When distance isn't taken into consideration, the numbers can be deceiving. A 26-putt round could represent a poor putting performance if a player had multiple chip-ins, while taking 32 putts could represent a good day on the greens. The strokes gained-putting statistic is one easily understood number that properly accounts for one-putts and three-putts from different distances, and it properly ignores chip-ins, the quality of iron shots and sand shots.
Based on your data for 2011, who are the Tour's top putters?
John Merrick gains an average of 1.046 putts per round on the field and is leading the Tour in strokes gained-putting in 2011. The best putters gain about one stroke per round against the field, or about four strokes per tournament. The worst putters lose about one stroke per round against the field. Here are the top 10 putters on Tour right now:
1. John Merrick, 1.046
2. Greg Chalmers, 1.033
3. Brandt Snedeker, 0.962
4. Steve Stricker, 0.941
5. Lucas Glover, 0.878
6. Jimmy Walker, 0.849
7. Nick Watney, 0.804
8. Luke Donald, 0.632
9. Kevin Na, 0.625
10. David Toms, 0.614
What players are currently being held back by their putting?
Here are some of the golfers who rank in the top 50 in FedEx Cup points or the money list but rank out of the top 100 in strokes gained:
J.B. Holmes, 105, -0.018
K.J. Choi, 110, -0.042
Bubba Watson, 115, -0.073
Jonathan Byrd, 126, -0.143
Jhonattan Vegas, 131, -0.174
Rory Sabbatini, 134, -0.212
Justin Rose, 135, -0.218
Dustin Johnson, 148, -0.376
Ricky Barnes, 151, -0.398
Adam Scott, 178, -0.827
These golfers are doing well this season, but putting has not been their strong suit. They are losing between 0 and 0.8 strokes per round to the field.
What is the future of this type of research?
The PGA Tour's ShotLink data is a treasure trove of information. I'm really excited about the potential for this amazing data to further our understanding and enjoyment of the game.